This application claims the benefit of Korean Application No. 2001-77577, filed Dec. 8, 2001, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an active steering system and a method thereof by which a belt can be steered so that additional registration correction is not needed which is used in an image forming apparatus, and a method of seeking a balance point at which the belt is driven most stably.
2. Description of the Related Art
In a system using a belt, a problem of weaving necessarily occurs during the driving of the belt. In particular, in an image forming apparatus of an electrophotography type such as printers, copiers, and facsimiles, weaving of the belt used as a photosensitive medium or transfer medium mainly causes mis-registration so that an image in a main scanning direction is deviated.
When the weaving of the belt used as the photosensitive medium or transfer medium occurs, mis-registration occurs where positions at a starting of the respective lines not being aligned within a page occurs. During formation of a color image, color mis-registration can occur so that color dots are not accurately overlapped. Thus, in the image forming apparatus adopting the belt as the photosensitive medium or transfer medium, a steering technology to control the position of the belt in a main scanning direction (a widthwise direction) is very important to prevent the weaving of the belt.
As shown in FIG. 1, a conventional registration system to control belt steering and scanning start points detects belt edge signals using laser beams emitted from four scanners 5a, 5b, 5c, and 5d and uses the belt edge signals, to prevent weaving of the belt and adjusts a deviation of the image due to the weaving of the belt. The four scanners 5a, 5b, 5c, and 5d scan the laser beams modulated according to image data onto a photoreceptor belt 1 supported by a plurality of rollers and endlessly circulating, to form an electrostatic latent image.
Referring to FIG. 1, in the conventional registration system, a belt edge sensor 3 includes four photodetectors 3a, 3b, 3c, and 3d, which are installed on an edge of the photoreceptor belt 1 to be overlapped. The four photodetectors 3a, 3b, 3c, and 3d receive the laser beams scanned by the scanners 5a, 5b, 5c, and 5d, respectively, and detect belt edge signals. Because part of the laser beams emitted from the scanners 5a, 5b, 5c, and 5d are blocked by the photoreceptor belt 1, the photodetectors 3a, 3b, 3c, and 3d receive only remaining portions of the laser beams which are not blocked by the photoreceptor belt 1. Thus, an amount of light received by the photodetectors 3a, 3b, 3c, and 3d changes according to a position of the photoreceptor belt 1 in the main scanning direction. The belt edge signals detected by the photodetectors 3a, 3b, 3c, and 3d convey information about the position of the photoreceptor belt 1.
The belt edge signals detected by the photodetectors 3a, 3b, 3c, and 3d are compared with a signal indicating a previous position of the photoreceptor belt 1 at a belt edge synthesizer 7. The belt edge synthesizer 7 generates a belt edge signal to change an image data start position of a corresponding line according to a change in position of the photoreceptor belt 1. The synthesized belt edge signal is converted into an image scan start signal 114 indicating an image data start position of a corresponding line at a scanner control/synchronization module 9. The image scan start signal changes a start position of the image for each line according to the weaving of the photoreceptor belt 1 so that the image can always maintain a predetermined distance from the edge of a print paper and multi-color dots are arranged to be overlapped at the same position of the photoreceptor belt 1. In FIG. 1, reference numeral 11 denotes a computer for controlling a laser drive using the image scan start signal and a signal output from a controller 13 to control the overall image forming apparatus so that the laser beam can be output modulated using signals from the laser drive 108, 110, and 112 and the image scan start signal 114 from the scanner control/synchronization module 9 according to the image data.
Meanwhile, the belt edge signal passing through the belt edge synthesizer 7 is input to a belt steering controller 15. The belt steering controller 15 drives a belt steering motor (not shown) according to the belt edge signal so that the edge of the photoreceptor belt 1 can be driven at the center of the photodetectors 3a, 3b, 3c, and 3d. 
The conventional registration system having the above structure controls the position of the photoreceptor belt 1 in the main scanning direction using a result obtained from Equation 1.
(Equation 1)
Y=Kpxc3x97(the present belt positionxe2x88x92the central position of photodetectors)+KDxc3x97(the present belt positionxe2x88x92the previous belt position)
Here, KP is a proportional coefficient and KD is a differential coefficient. The Y value obtained from Equation 1 is used as a driving step number of a belt steering motor. When the belt steering motor drives a steering roller by a predetermined step according to the Y value, the steering roller is slant. Accordingly, a direction of movement of the photoreceptor belt 1 in the main scanning direction changes.
FIGS. 2 and 3 are graphs showing results of tests using the conventional registration system by changing the KP and KD values. FIG. 2 is a graph showing the output of a photodetector measuring an amount of change of the belt edge when KP and KD are 1 and 15, respectively. FIG. 3 is a graph showing the output of the photodetector when KP and KD are 0.5 and 10, respectively. To obtain the results of FIGS. 2 and 3, a product xe2x80x9cPD S6967xe2x80x9d having a length of 5 mm manufactured by HAMAMATSU is used as the photodetector. The maximum output voltage is set to 5 volts such that 1 volt corresponds to 1 mm in the weaving width of the belt. The photodetector is installed at the position separated 6 seconds from the belt steering apparatus. A 32 inches long sheet is used by being attached to the photoreceptor belt 1. Here, a step of a seam is about 330 xcexcm, a parallelism thereof is 51 xcexcm, and a drive speed of the belt is 3.2 inch/sec. To reduce an effect due to any defect of the photoreceptor belt 1, an output of the photodetector is accumulated for ten seconds.
Maximum weaving widths obtained from the above test conditions are 460 xcexcm and 291 xcexcm, respectively, as shown in FIGS. 2 and 3. The amounts of weaving with respect to the movement speed of the photoreceptor belt 1 are 3 xcexcm/sec and 2 xcexcm/sec, which means that, in the case of continuous printing, mis-registration of 300 xcexcm (corresponding about 6 dots in the case of 600 dpi) or more from the edge of the paper to the image can be generated. Thus, when the conventional registration system is adopted, the scanning start point must be controlled in addition to the belt steering.
Because since the conventional registration system includes four photodetectors 3a, 3b, 3c, and 3d which receive laser beams scanned by scanners 5a, 5b, 5c, and 5d to form the image by color, and because calculations for the belt steering and color registration correction is performed at the belt edge synthesizer 7 using the belt edge signal for each color detected by the four photodetectors 3a, 3b, 3c, and 3d, the structure of the system is complicated and complicated calculations must be performed at the belt edge synthesizer 7.
When there is a defect at the edge of the photoreceptor belt 1 or the step of the seam generated by connecting the photoreceptor belt 1, a belt error signal is detected as if the position of the photoreceptor belt 1 is moved. To minimize the belt error signal, the outputs of the photodetectors 3a, 3b, 3c, and 3d are accumulated as long as the period of the photodetector belt 1 and the accumulated value are used as values of a present position of the photoreceptor belt 1.
Thus, in the conventional registration system, because the adjustment of the position of the photoreceptor belt 1 in the main scanning direction is delayed as long as the output of the photodetectors 3a, 3b, 3c, and 3d are accumulated for the period of the photoreceptor belt 1, the amount of weaving increases.
Also, in the conventional registration system, because the laser beams output from the scanners 5a, 5b, 5c, and 5d to form the an electrostatic latent image are used as the light source to detect the belt edge signals, the system can only be applied to the structure in which the photoreceptor belt 1 is used.
Further, in the conventional registration system, because the laser beam needs to be scanned for the photodetectors 3a, 3b, 3c, and 3d disposed out of an image area on the photoreceptor belt 1, the distance that the laser beam is scanned increases. Accordingly, the size of an optical element such as a mirror or a lens in the scanners 5a, 5b, 5c, and 5d should be increased.
To solve the above-described problems, in accordance with an aspect of the present invention, there is provided an active steering system and a method thereof which can minimize an amount of weaving of a belt by steering the belt based on a balance point at which the belt is driven most stably so that no additional registration correction is needed when the system and the method are applied to an image forming apparatus. There is also provided a method of seeking a balance point at which the belt is driven most stably.
In accordance with an aspect of the present invention, there is provided an active steering system including a drive source; a steering roller adjusting a belt in a widthwise direction, which is rotated by the drive source; a steering motor driving the steering roller; a steering controller controlling the steering motor; a belt edge sensor detecting a belt edge signal according to a position of the belt in the widthwise direction; and a main controller controlling the drive source and/or the steering controller where the belt is rotated based on a balance point at which an amount of change of at least one value of the belt edge signal and a step number of the steering motor is less than or equal to a predetermined value.
In accordance with an aspect of the present invention, when an average of step numbers of the steering motor for a predetermined time does not change within a predetermined range of allowance, a position corresponding to the average of the step numbers is set as the balance point.
In accordance with an aspect of the present invention, the predetermined time is a period of time the belt rotates one time.
In accordance with an aspect of the present invention, while the belt is rotated with respect to the balance point, the belt is controlled where the edge is located at a center of the photodetector.
In accordance with an aspect of the present invention, the active steering system further includes a memory storing data of the balance point.
In accordance with an aspect of the present invention, the balance point changes according to an operation of at least one sub-unit affecting the balance point, where the at least one sub-unit is installed in a predetermined apparatus to which the active steering system is applied, and is measured in advance and stored in the memory, and the belt is steered according to the balance point fit to the operation of the sub-unit.
In accordance with an aspect of the present invention, the belt is one of a photoreceptor belt, a transfer belt, a drying belt, a fusing belt, and a conveyance belt.
In accordance with an aspect of the present invention, the steering motor is driven at a predetermined step interval.
In accordance with an aspect of the present invention, the steering motor is driven at a larger step interval as the belt is located far away from a reference position with respect to the balance point, and at a smaller step interval as the belt is located close to the reference position.
In accordance with an aspect of the present invention, the steering motor is driven at a step interval at which a relationship between the belt edge signal and the step number of the steering motor satisfies a quadratic function.
In accordance with an aspect of the present invention, the light source includes at least one light emitting diode.
In accordance with an aspect of the present invention, there is provided a method of actively steering a belt in an active steering system including a drive source, a steering roller to adjust a belt in a widthwise direction which is rotated by the drive source, a steering motor to drive the steering roller, a steering controller to control the steering motor, a belt edge sensor to detect a belt edge signal according to a position of the belt in the widthwise direction, and a main controller to control the drive source and/or the steering controller where the belt is rotated based on a balance point at which an amount of change of at least one value of the belt edge signal and a step number of the steering motor is less than or equal to a predetermined value, the method including: according to the control of the main controller, driving the steering motor to move the steering roller to the balance point at which the amount of change in the at least one value of the belt edge signal and the step number of the steering motor is less than or equal to the predetermined value, and driving the drive source to rotate the belt in a proceeding direction; comparing the belt edge signal detected and a reference belt edge signal detected when the steering roller is located at the balance point; and when the belt edge signal is different from the reference belt edge signal, determining the step number of the steering motor changing from a reference step number with respect to the balance point, which corresponds to a degree of the belt edge signal deviating from the reference belt edge signal, and adjusting the position of the belt in the widthwise direction by moving the steering motor to the step number, wherein the position of the belt in the widthwise direction is controlled by repeating the comparing of the belt edge signal and the determining of the step number of the steering motor during the rotation of the belt.
In accordance with an aspect of the present invention, the belt edge sensor includes a light source, and a photodetector provided across at least one side edge of the belt where an amount of a light received, which is emitted from the light source, changes according to the position of the belt in the widthwise direction, and, when the steering roller is located at the balance point, the edge of the belt is controlled to be located at a center of the photodetector.
In accordance with an aspect of the present invention, where the seeking of the balance point occurs when the belt is newly installed or replaced, or when the balance point is changed.
In accordance with an aspect of the present invention, when an average of the step numbers of the steering motor for a predetermined time is the same as an average previously obtained within a predetermined range of allowance, a position of the steering roller corresponding to the average of the step numbers is set as a balance point.
In accordance with an aspect of the present invention, the predetermined time is a period of time the belt rotates one time.
In accordance with an aspect of the present invention, the balance point changes according to an operation of at least one sub-unit affecting the balance point, where the at least one sub-unit is installed in a predetermined apparatus to which an active steering system is applied and is measured in advance and stored in the memory, and the belt is steered with respect to the balance point fit to the operation of the sub-unit.
In accordance with an aspect of the present invention, there is provided a method of seeking a balance point at which a belt is driven stably to steer the belt using an active steering system, which includes a drive source, a steering roller to adjust a belt in a widthwise direction which is rotated by the drive source, a steering motor to drive the steering roller, a steering controller to control the steering motor, a belt edge sensor to detect a belt edge signal according to a position of the belt in the widthwise direction, and a main controller to control the drive source and/or the steering controller where the belt is rotated based on a balance point at which an amount of change of at least one value of the belt edge signal and a step number of the steering motor is less than or equal to a predetermined value, the method including: when the amount of the change of the at least one value of the belt edge signal and the step number of the steering motor is less than or equal to a value, obtaining an average by averaging the step numbers of the steering motor for a predetermined time; comparing the average of the step numbers and an average of the step numbers previously obtained; and when the average of the step numbers is the same as the average previously obtained of the step numbers within a predetermined range of allowance, determining a position of the steering roller corresponding to the average of the step numbers as the balance point.
In accordance with an aspect of the present invention, the seeking of the balance point is performed in a case in which the steering roller is moved to a position corresponding to a middle value of a step range of the steering motor or the step number corresponding to a previous balance point by driving the steering motor.
In accordance with an aspect of the present invention, the seeking the balance point is performed when the belt is newly installed or replaced, or when the balance point is changed.
In accordance with an aspect of the present invention, the method further includes storing the sought balance point.
In accordance with an aspect of the present invention, the driving of the steering motor, the comparing of the belt edge detected, and the determining of the step number are repeated by changing an operational state of at least one sub-unit to seek a first balance point when there is no effect by an operation of the sub-unit and a second balance point changed during the operation of the sub-unit, where an optimal belt steering can be performed even when the balance point is changed according to the operation of the sub-unit affecting the balance point, which is installed in an apparatus to which the active steering system is applied.
In accordance with an aspect of the present invention, the seeking the second balance point is repeated as many times as a number of balance points changed according to the operation of the sub-unit.
In accordance with an aspect of the present invention, there is provided a method of an active steering system, including: minimizing an amount of weaving of a belt by steering the belt based on a balance point at which the belt is driven most stably where no additional registration correction is needed when applied to an image forming apparatus.
These together with other aspects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part thereof, wherein like numerals refer to like parts throughout.